Is RwTxn Send?

I found that multi-threaded tokio runtime moves the task between threads, and this leads to let tx = env.write_txn() and tx.commit() to run in different threads. And the next call to env.write_txn() hangs.

let tx = env.write_txn()?; // thread A

while let Some(row) = stream.next().await {
    insert_row(&mut tx, row)?;
}

tx.commit()?;  // thread B

let tx = env.write_txn()?;  // hangs

[indexing] IndexBuilder tx is created in thread=ThreadId(9)
████████████████████████████████████████ 4317834/4317834
[indexing] IndexBuilder tx is committed in thread=ThreadId(17)
[task] lmdb - getting WriteTx in thread=ThreadId(17)  # hangs

Switching to a single-threaded tokio runtime did not have a deadlock.

I found this in https://github.com/jnwatson/py-lmdb/issues/89#issuecomment-109167232 :

A write Transaction can only be used from the thread it was created on.

Is it okay to commit a write transaction in a different thread?
If not, what is a recommended approach to interleave async workload with transactions?

Start with the multi-threaded Tokio reproducer shown in the issue and trace the write_txn and commit calls across the reported thread changes. Check the transaction API and LMDB thread-safety expectations, then determine the supported approach for interleaving async work with transactions. Done means the cross-thread commit behavior and a recommended usage pattern are clearly established.